The fact that engine oil becomes dark over time is taken for granted by most car enthusiasts. Much more contradictions can be found online if we are talking about too rapid contamination of the lubricant. Opinions vary greatly here - some argue that there is nothing to worry about, especially if the power unit is old, others believe that this is a sign of an impending disaster that requires immediate response. We will try to describe this problem in as much detail as possible, using a multi-aspect approach - this way the reader will have a more objective opinion about the problem.
Darkened engine oil
Why does the oil darken?
First, let's try to find out how the MM generally works in a power unit. It is intuitively clear that this fluid is used to prevent premature wear of the rubbing surfaces of engine parts. But this is not the only function of the oil: it also acts as an adsorbent that cleans the engine surfaces from technical contaminants that are inevitable during the operation of the car. Since motor oil itself does not have adsorbing properties, special additives are introduced into it that change the alkaline number of the liquid.
Black oil in the engine indicates that the alkali is still performing its functions - neutralizing acids, and also rids the engine of carbon deposits and other pollutants. Since the lubrication system is by definition sealed, all this dirt ends up in the lubricant. Partially it settles on the oil filter, but it is not able to catch the smallest particles. So the color of the oil quickly changes to a darker one, and the more worn out the power unit is, the more clearly this dependence manifests itself.
But when a lubricant retains its color for a long time, this is a reason to think about whether it copes with its cleaning duties? Most likely, no, which means that either you deliberately purchased cheap oil of dubious quality, or you came across a fake, of which there are a dime a dozen on the market today. Due to the lack of high-quality additives, such a liquid performs only lubricating functions. And even those, most likely, are not doing it properly.
The “correct” oil is characterized by a sufficient alkaline number, which helps prevent two main causes of premature wear of the power unit:
- oil deficiency, which is a consequence of blockage of the channels with contaminants that prevent normal fluid circulation;
- deterioration of heat dissipation, which results in overheating of the motor with all the ensuing negative consequences. In particular, local overheating causes rotation of the liners, deformation and destruction of the camshaft, and other equally dangerous consequences.
But not everything is so simple. A high alkaline number, it turns out, in certain cases brings tangible harm instead of benefit. Such cases, first of all, should be understood as ignoring routine lubricant replacement. With prolonged use, the adsorption additive, resisting heavy engine contamination, gradually loses its cleaning properties.
So you shouldn’t be surprised at the darkening of the color of an initially light and transparent product: this is a natural process. In some cases, the engine oil turns black quickly, sometimes over a fairly long period of time, but in any case the color changes to a darker one. The speed of the process initially says little, since it depends on many diverse factors, the main of which are:
- the condition of the engine, how regularly the routine procedures were performed;
- what is the concentration of detergent additives in the currently used product;
- How long ago did you replace the MM and oil filter?
The older the power unit, the more various deposits have accumulated in it, so after adding fresh fluid it darkens faster than on a relatively new engine. The rate of color change directly depends on the amount of alkaline additives, which in different brands of oils can differ by a noticeable amount.
The faster darkening of engine oil in a diesel engine is due to the characteristics of diesel fuel, which contains much more substances that generate soot during combustion. For this reason, the oil on such engines turns black almost immediately, and this fact should be known to every owner of a car with a diesel power unit.
If you are convinced that the rate of the process is too fast, you have two ways of performing an experiment that will help establish the truth:
- using higher quality branded oil, the quality of which you can be sure of;
- more frequent replacement of lubricant (about 20-30% more often than the automaker recommends).
But such a step should be taken only in cases where the contamination of the lubricant is not critical, that is, it does not create problems that threaten the condition of the power unit. But when this process is accompanied by malfunctions in the engine, you should first perform a thorough diagnosis of all its systems and components, which will indicate the possible cause of rapid contamination of the fluid.
Blackened oil on the dipstick
You can try to reduce the rate of contamination of the lubricant by flushing the engine with special mixtures that can clean the internal surfaces of the engine from deposits that oil cannot remove. But you can’t overdo it here, since such compounds have a destructive effect on rubber parts and seals. In addition, it is impossible to predict in advance the reaction of the base lubricant to mixing with the cleaning solution - in a negative scenario, the MM will lose a significant part of its characteristics.
We list the factors that have the greatest impact on the rate of darkening of engine oil:
- crankcase gases entering the engine. Problems in the system for getting rid of crankcase gases lead to the fact that some of them penetrate back into the CPG, where they can come into contact with the engine oil. As a result, the lubricant oxidizes, losing its performance characteristics and quickly changing color to dark. If the malfunction is significant, the speed of this process increases rapidly;
- wear of the piston group. The main consequence of this phenomenon is the loss of tightness of the CPG, as a result of which lubricant that should not be there begins to enter the combustion chamber, and fuel begins to enter the crankcase of the power unit, diluting the lubricating technical fluid. The oil eventually loses its original lubricating and cleaning properties, increasing wear of rubbing parts and its own contamination. Diagnosing this problem is quite simple: you just need to wipe the oil dipstick with a clean, light cloth. The presence of deep black stains will indicate a phenomenon such as lubricant waste, which occurs as a result of its combustion in the cylinders. When the gaps increase due to engine wear, you can observe increased MM consumption, problems with starting the engine, and a high degree of smoke in the exhaust;
- high ash content and TBN. Sulfate ash content is an indicator that characterizes the quantitative content of elements in the oil that do not burn. It directly correlates with the base number, abbreviated TBN. This means that the higher the ash content, the faster the lubricant will darken during operation. This cannot be called a disadvantage - high cleaning abilities are welcome, however, when choosing oil, you should focus on the indicators recommended by the car manufacturer, trying not to exceed them unnecessarily. You also need to understand that a lubricant with a low alkalinity is very sensitive to the quality of the fuel and quickly loses its cleaning properties. For this reason, such a MM should be replaced much more often - approximately every 7-7.5 thousand kilometers;
- Engine overheating is another reason why the engine oil darkens much faster. Such consequences result from operating the vehicle in an aggressive mode with prolonged increased loads. The cause of overheating may be a coolant leak, as well as a malfunction of the thermostat or water pump, or air pockets in the cooling system line.
Causes
As you know, any lubricant for internal combustion engines may contain additives. Moreover, there can be many of them and each of them is introduced into the composition of the consumable material for a specific purpose. In particular, these can be chemical elements responsible, for example, for reducing friction of engine elements, temperature properties, viscosity, and so on.
Dipstick for checking lubricant level with residual black oil
And one of these additives is a substance responsible for the alkaline index. And not without reason, because alkali is a very important element in the composition of any lubricant. In particular, it eliminates chemicals that can enter the lubrication system during operation of the motor fluid. In addition, alkali prevents the appearance of sediments and deposits in the engine, while simultaneously removing all dirt and harmful deposits.
But if there is not enough alkali in the MM, then the engine will wear out much faster and, accordingly, will become clogged with all kinds of sediments and deposits. This means that the oil quickly turns black in the engine is not surprising. So, let’s consider in general the reasons why the MM can quickly darken in the engine:
- as we have already figured out, this is a lack of alkaline number in the composition of the lubricant;
- the entry of combustion and oxidation products into the lubrication system as a result of physical wear of the cylinder-piston group;
- directly poor quality of consumables (don’t be surprised if you bought MM from some suspicious seller on the side of the road);
- or it can be an expensive and high-quality consumable material that washes away deposits and sediments formed in the vehicle’s internal combustion engine during oil operation.
Black waste liquid
When dark oil is normal
The automotive lubrication system is a closed, sealed circuit. Draining into the crankcase, the oil is then delivered by a pump to the main channels passing through the lubricated parts. Along the way, it absorbs oxides, mechanical particles formed during friction, as well as carbon deposits, and returns to the crankcase. It is not surprising that, constantly enriched with various pollutants, it darkens.
Since the parts of the power unit operating in extreme speed conditions become very hot, a significant part of the heat is transferred to technical fluids - antifreeze and engine oil. The latter can heat up to temperatures exceeding 100°C. This is good for the lubricant - it becomes more fluid, which allows it to penetrate into technical gaps, reducing friction and washing away fresh carbon deposits that have not yet coked. This natural darkening is called “oil work.”
So if, after prolonged use, the MM has practically not changed its color, they say that the lubricant does not work. At least this concerns its cleansing characteristics. In this case, all deposits remain on the walls of the engine, forming a rather thick layer of indelible carbon deposits, which, firstly, changes the size of the technological gaps and the geometry of engine components, and secondly, impairs the heat transfer of the power unit, which leads to prolonged operation at elevated temperatures . Figuratively speaking - to overheating. Consequently, the car owner uses a frankly low-quality product, a fake, which reduces the life of the engine.
Black oil in the engine is not a cause for concern if the dark color acquired gradually over the regulatory interval. Thus, if the lubricant after driving 5,000-10,000 kilometers has generally retained its original performance characteristics, but has darkened, this is normal, this is an indicator that the oil used is appropriate for the specific engine.
If the oil in the engine turns black, this only means that all pollutants, including compounds spent during the combustion process of fuel assemblies, enter the lubricating fluid without lingering on the walls of the working area. This protective ability of motor oil minimizes the likelihood of oxidative reactions occurring inside the power unit, increasing its service life. During a scheduled oil change during the next maintenance, all substances washed out by the lubricant are drained, and clean oil is poured into the system.
conclusions
1. A change in oil color indicates the following:
- darkened - everything works fine, the engine is safe;
- light - the selected lubricant does not perform its functions, it needs to be replaced;
- black - indicates a breakdown and the need for vehicle diagnostics.
2. The rate at which the oil darkens does not affect its protective and lubricating functions, but it is better to replace it before the due date.
3. A high-quality, high-alkaline lubricant product has short replacement intervals and must be used carefully, especially for older engines.
Gradual engine cleaning
As we found out, a change in the shade of the oil is the result of the ingress of pollutants formed in the engine during its intensive operation. High-alkaline additives also make their contribution. A color that is too dark does not mean that there are problems with the power unit; this is a completely normal natural process, but if the MM becomes very dark, it should be replaced along with the oil filter, without waiting until the numbers corresponding to those given in the operating manual appear on the speedometer. If your goal is to gradually clean the engine of accumulated contaminants, change the oil filter not only when changing the oil, but also in between, at least once. It's not such an expensive method that you shouldn't try it.
Draining the black MM from the engine
It is safe to say that slow cleaning of the engine from suspended microparticles is much more useful than the express method based on the use of detergent additives with aggressive components, which, when mixed with oil, worsen its technical parameters (in particular, viscosity).
More liquid lubricant flows faster into the sump, without lingering in the working areas, which causes faster wear of engine components that need high-quality lubrication.
Many car owners refuse the gradual cleaning method, considering it too expensive. In fact, more frequent replacement of the MM will initially lead to the fact that over time it will become dirty much more slowly, returning to the indicators that were observed when the power unit was young.
For old, heavily worn engines, one of the most typical causes of accelerated darkening of the lubricant is the ingress of combustion products, that is, crankcase gases, into the oil. This problem is easily diagnosed, since this process is accompanied by the appearance of a very specific and recognizable smell of burnt MM in the engine compartment. This will also be evidenced by an increase in its consumption, as well as an increase in fuel consumption.
The problem is treated by replacing the piston rings, and in especially severe cases, by replacing the boring sleeves, which allows them to be given their original standard dimensions.
Another good way to prevent premature contamination of the lubricant is to regularly top it up when the level decreases, until it is time for a scheduled replacement.
Most experienced car owners claim that when using high-quality lubricating fluid, it begins to darken after fairly significant runs, about 7-10 thousand kilometers. If the initial alkalinity index is high, when such oil darkens, no destructive processes occur in the engine. The dark color in this case is evidence that the lubricant managed to absorb the maximum amount of harmful deposits accumulated on the surface of the engine parts. There is no need to rush into replacing; carry out this activity in accordance with the recommended dates.
What can you do?
- To be sure of the quality of the lubricating fluid, it is better to choose products from trusted brands. Surely it will cost more, but remember that the costs of major repairs are more significant.
- Do not neglect the recommendations of the automaker that produced the car. The technical documentation indicates with what characteristics the oil should be poured into the power unit.
- It is better not to change the brand of lubricant without good reason. This may be required only if the flooded one does not cope with its tasks.
- Flush the engine periodically. For this purpose, special compounds are used. Their peculiarity is the increased content of detergent additives. This procedure is required when changing the brand of oil. It allows you to remove dirt and remnants of the old composition.
- Don't neglect regular oil changes. They should be performed in accordance with the manufacturer's instructions. At the same time, you need to change the filters and make the necessary adjustments to the functioning of the systems.
The gradual darkening of engine oil is a natural process that will have little effect on the performance of the internal combustion engine. However, if blackening occurs rapidly and intensely, then it is worth contacting a car service to diagnose and identify the cause. In order not to harm the car’s power unit, you should follow the manufacturer’s recommendations and choose lubricating products from responsible brands.
Consequences of long-term driving on black oil
The roots of the misconception of many motorists regarding the color of MM, which manifests itself in the form of aversion to the black color of the lubricant, should be sought in the Soviet past, when the quality of the oil was directly associated with its color, and this was fair. But it was a long time ago. Today, even outright counterfeit products have a transparent consistency and a light shade.
If, after long-term operation of the engine, the oil darkens slightly, this indicates either that the engine is not very dirty, or that the alkalinity level is not high enough. In the latter case, the lubricating properties of the liquid are not affected in any way, but the cleaning properties are frankly insufficient.
Dark MM indicates that it properly performs cleaning functions, but the functionality of such a lubricant is sharply reduced. If you continue to drive with such oil, it will no longer be able to wash away pollution products from the surface of the power unit parts, contributing to the thickening of the carbon layer on key engine components.
Consequences of blackening engine oil
We diagnose the problem in a timely manner
Comparison of fresh/used/old oil
To understand whether the fuel darkens quickly or, conversely, remains crystal clear, it is necessary to regularly assess its condition using an oil dipstick. The check should be carried out 1-2 times a week in order to promptly recognize the problem.
Please note that before analyzing the color, consistency and level of the lubricant, it is necessary to wipe the dipstick only with a clean cloth. If thread fibers, spools or other debris enter the working area, it will quickly contaminate the technical fluid.
Recommendations
Lubricants should only be purchased in specialized stores. It is better to come to the scheduled technical inspection with your own oil, having first checked whether it produces sediment.
Check the level and condition of the lubricant using the oil dipstick.
You can periodically check the condition of the oil using the “drop test” method. To do this, you will need porous paper (any kind of paper will do, even a piece of newspaper). After the engine has cooled, you need to drip some lubricant from the oil dipstick onto the paper. Normal oil should spread across the paper, forming circles. But if it forms a thick black drop, then it needs urgent replacement.
